Final answer:
The most critical assessment finding to report after deflating a Sengstaken-Blakemore tube is evidence of rebleeding or hemorrhage.
Step-by-step explanation:
The most important assessment finding by the nurse after the deflation of the esophageal balloon that should be reported to the health care provider (HCP) immediately would be any evidence of rebleeding or hemorrhage. This could present as fresh bleeding from the mouth or nose, signs of hypovolemic shock such as rapid pulse, low blood pressure, or changes in consciousness. The Sengstaken-Blakemore tube is designed to control esophageal varices bleeding, and upon deflation, the priority is to ensure that this bleeding does not recur, as it can be life-threatening.